In conventional web inspection machines, regardless of the means of error detection, the fundamental requirement is to locate the position of an error along the length of the web, and subsequently to decelerate and stop the machine in such a manner that the error is positioned at a “splicing station” where it may be corrected by the operator. Several methods are conventionally used to achieve this requirement.
A first method, for use with unidirectional machines that cannot be reversed, involves providing a sufficient distance along the web path between the inspection zone and the splice station to enable the section of the web with the detected error to be stopped at, or prior to, the splice station. If the error passes by the splice station it cannot be brought back to the splicing area because the machine is not capable of reversing the movement of the web.
An example of such a machine is described in my U.S. Pat. No. 3,733,230, the disclosure of which is incorporated herein by reference. While the web flow path in this machine design has been used in many thousands of machines, it suffers from drawbacks with respect to the manufacturing and processing demands of industry today.
Firstly, the industry is demanding that web inspection machines be capable of handling much larger unwind rolls. Since, in the web flow path of the machine shown in FIG. 4 of U.S. Pat. No. 3,733,230, the web travels from the inspection zone around the unwind roll to reach the downstream fault splicing table at the left-hand side of the machine, making the unwind roll larger would force the machine designer to raise the inspection zone to an impractical height.
Secondly, the industry is also demanding that web inspection machines be capable of rewinding much larger rolls for later delivery in larger volumes to clients. The web path layout of the machine design shown in FIG. 4 in U.S. Pat. No. 3,733,230 also greatly limits the diameter to which finished rolls can be practically wound.
Thirdly, the operator of a web inspection machine such as shown in FIG. 4 of U.S. Pat. No. 3,733,230, after having detected a fault in the inspection zone and stopped the machine, must move from the inspection zone to the far left-hand end of the machine to remove or replace the fault. This need to move back and forth between the inspection zone and the fault splicing area can be quite time consuming, especially if there are many faults to correct in the unwind roll or in the web, which are caused during subsequent downstream imaging or converting processes or functions occurring upstream of the inspection zone.
When a reversing machine is utilized, the web can be wound back onto the unwind mandrel of the machine. However, this option is often compromised by another function of the machine, for example, in line imaging or converting or slitting of the web just prior to passing into the machine rewind. Once the web is slit, it normally cannot be reversed through the slitter. For this reason, bidirectional machines are generally only used where imaging or converting or slitting is not required. Alternatively, the slitting is done on a second (post inspection) pass at a higher cost. Also, a reversing machine can often encounter difficulties with web guiding.
A third method involves the reversed retrieval of a fault (once detected and stopped by the operator or the machine) back to a combined inspection/splicing area for fault repair without having to move the unwind roll or the rewind roll. This involves the addition of a “double festoon” which is connected in such a fashion as to deplete a long length of web from one section of the machine and to add a long length of web to another section of the machine.
An example of such a machine is described in my U.S. Pat. No. 5,727,748, the disclosure of which is incorporated herein by reference, which requires a substation of the machine to be moved in order to retrieve a previously searched for fault to a combined inspection/splicing area, as seen in FIG. 5 of U.S. Pat. No. 5,727,748.
This method requires the addition of considerable web length to the machine at very considerable machine and web cost. Also, when the shuttle mechanism of the double festoon is activated, web guiding difficulties are often encountered. Also, this method often puts unacceptable limitations on the types of materials that can be processed and the diameters from which and to which they can be processed.
When a web inspection machine has been equipped with a slitting system, or another converting function such as image printing or die cutting, it is highly desirable that the operator be able to see both the web passing through the inspection zone and the web being slit (and rewound) at the same time and in close proximity. This requires the close physical location of the inspection zone with respect to the slitting and rewinding areas of the machine. One such machine design, which is shown in FIG. 1 hereof, provides the inspection zone located in close proximity, such as above and just to the left of the slitting and rewinding areas of the machine. This allows the operator to view the web passing through the inspection zone while also being able to see the slitting and rewinding areas in the same field of view. When the operator detects a web fault in the inspection zone he stops the machine. Depending upon the running speed of the machine, the web length between the inspection zone and the splicing area, and the operator's reaction time, the fault (when the machine has come to a stop) will be located at a point between the inspection zone and the fault splicing table. Then the operator can jog the web fault forward to the splice table for fault removal or repair.